to be better or more effective as a group than you would think just by looking at the individual members of the group
BE GREATER / MORE THAN THE SUM OF ITS PARTS
Meaning of BE GREATER / MORE THAN THE SUM OF ITS PARTS in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005